WordPress BEM Menu Walker

bem_wp_menu.php

<?php

class Bem_Menu_Walker extends Walker_Nav_Menu {
  /**
   * Starts the list before the elements are added.
   *
   * @see Walker::start_lvl()
   *
   * @since 3.0.0
   *
   * @param string $output Passed by reference. Used to append additional content.
   * @param int    $depth  Depth of menu item. Used for padding.
   * @param array  $args   An array of arguments. @see wp_nav_menu()
   */
  public function start_lvl( &$output, $depth = 0, $args = array() ) {
    $block = isset( $args->block ) ? $args->block : explode(' ', $args->menu_class);
    $block = is_array( $block ) ? $block[0] : $block;
    $indent = str_repeat("\t", $depth);
    $output .= "\n$indent<ul class=\"${block}__sub-menu\">\n";
  }

  /**
   * Ends the list of after the elements are added.
   *
   * @see Walker::end_lvl()
   *
   * @since 3.0.0
   *
   * @param string $output Passed by reference. Used to append additional content.
   * @param int    $depth  Depth of menu item. Used for padding.
   * @param array  $args   An array of arguments. @see wp_nav_menu()
   */
  public function end_lvl( &$output, $depth = 0, $args = array() ) {
    $indent = str_repeat("\t", $depth);
    $output .= "$indent</ul>\n";
  }

  /**
   * Start the element output.
   *
   * @see Walker::start_el()
   *
   * @param string $output Passed by reference. Used to append additional content.
   * @param object $item   Menu item data object.
   * @param int    $depth  Depth of menu item. Used for padding.
   * @param array  $args   An array of arguments. @see wp_nav_menu()
   * @param int    $id     Current item ID.
   */
  public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
    $indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';
    $this->prepare_el_classes( $item, $args, $depth );
    $classes = empty( $item->classes ) ? array() : (array) $item->classes;

    /**
     * Filter the CSS class(es) applied to a menu item's list item element.
     *
     * @param array  $classes The CSS classes that are applied to the menu item's `<li>` element.
     * @param object $item    The current menu item.
     * @param array  $args    An array of {@see wp_nav_menu()} arguments.
     * @param int    $depth   Depth of menu item. Used for padding.
     */
    $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args, $depth ) );
    $class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';

    $output .= $indent . '<li' . $class_names .'>';
    $atts = array();
    $atts['title']  = ! empty( $item->attr_title ) ? $item->attr_title : '';
    $atts['target'] = ! empty( $item->target )     ? $item->target     : '';
    $atts['rel']    = ! empty( $item->xfn )        ? $item->xfn        : '';
    $atts['href']   = ! empty( $item->url )        ? $item->url        : '';

    /**
     * Filter the HTML attributes applied to a menu item's anchor element.
     *
     * @since 3.6.0
     * @since 4.1.0 The `$depth` parameter was added.
     *
     * @param array $atts {
     *     The HTML attributes applied to the menu item's `<a>` element, empty strings are ignored.
     *
     *     @type string $title  Title attribute.
     *     @type string $target Target attribute.
     *     @type string $rel    The rel attribute.
     *     @type string $href   The href attribute.
     * }
     * @param object $item  The current menu item.
     * @param array  $args  An array of {@see wp_nav_menu()} arguments.
     * @param int    $depth Depth of menu item. Used for padding.
     */

    $atts = apply_filters( 'nav_menu_link_attributes', $atts, $item, $args, $depth );
    $attributes = '';
    foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                    $value = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
                    $attributes .= ' ' . $attr . '="' . $value . '"';
            }
    }
    $item_output = $args->before;
    $item_output .= '<a'. $attributes .'>';
    /** This filter is documented in wp-includes/post-template.php */
    $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
    $item_output .= '</a>';
    $item_output .= $args->after;
    /**
     * Filter a menu item's starting output.
     *
     * The menu item's starting output only includes `$args->before`, the opening `<a>`,
     * the menu item's title, the closing `</a>`, and `$args->after`. Currently, there is
     * no filter for modifying the opening and closing `<li>` for a menu item.
     *
     * @since 3.0.0
     *
     * @param string $item_output The menu item's starting HTML output.
     * @param object $item        Menu item data object.
     * @param int    $depth       Depth of menu item. Used for padding.
     * @param array  $args        An array of {@see wp_nav_menu()} arguments.
     */
    $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
  }

  /**
   * Ends the element output, if needed.
   *
   * @see Walker::end_el()
   *
   * @since 3.0.0
   *
   * @param string $output Passed by reference. Used to append additional content.
   * @param object $item   Page data object. Not used.
   * @param int    $depth  Depth of page. Not Used.
   * @param array  $args   An array of arguments. @see wp_nav_menu()
   */
  public function end_el( &$output, $item, $depth = 0, $args = array() ) {
    $output .= "</li>\n";
  }

  public function prepare_el_classes( &$item, $args = array(), $depth = 0 ) {
    $block = isset( $args->block ) ? $args->block : explode(' ', $args->menu_class);
    $block = is_array( $block ) ? $block[0] : $block;
    $classes = array( $block . '__item' );

    if ( $item->current )
      $classes[] = $block . '__item--current';

    if ( $item->current_item_ancestor )
      $classes[] = $block . '__item--ancestor';

    if ( $item->current_item_parent )
      $classes[] = $block . '__item--parent';

    if ( in_array( 'menu-item-has-children', (array) $item->classes ) )
      $classes[] = $block . '__item--has-children';

    if ( $depth )
      $classes[] = $block . '__item--child';

    $item->classes = $classes;
  }
}

// Example
wp_nav_menu(array(
  'theme_location' => 'primary',
  'walker' => new Bem_Menu_Walker,
  'block' => 'navigation'
));